Rotary lawn mowers having a rigid blade with sharpened edges and a power source rotating the blade in a horizontal plane are well known. The blade is located inside a housing having a top wall and side walls which define an enclosed cutting chamber that contains the blade. This type of mower cuts standing vegetation by the action of the sharpened edges contacting the vegetation as the mower is moved over the ground. Thus, a relatively high blade speed is required for efficient cutting. This high speed of rotation, in conjunction with the rigidity of the blade, necessitates that the blade be inside the housing to avoid injury to the operator or bystanders, or damage to property, either from direct contact with the blade or from missiles thrown by the blade.
Because the housing side walls extend beyond the end of the blade, with their lower edge being usually slightly below the plane of cut, mowers of this type cannot be used for close-in trimming along foundations, walls, trees, and the like, thereby leaving unsightly, uncut vegetation adjacent these objects. This uncut vegetation must then be trimmed manually, which is a laborious and time-consuming process; or with a trimming device which uses a spinning flexible line. This latter method, while reasonable effective, requires the added expense of a second machine for the trimming function, and the inconvenience and additional time required for trimming after the original mowing operation.
Filament mowers have recently been introduced. some of which utilize various means to provide a trimming as well as cutting capability. One such device is disclosed in U.S. Pat. No. 4,232,505, assigned to The Toro Company, the assignee of the present invention. This device is presently produced and marketed by The Toro Company as the Toro Mower/Trimmer. In this purely filament mower, the filament continuously extends outwardly through cut out portions of the side walls of the housing. The disadvantages of this type of device are that the filament is always extending out past the housing even when mowing, which results in premature wear of the line, and the necessity for frequent replenishment. In addition, it may not always be desirable to have the cutting element extending beyond the housing, such as when operating near flowers, young trees, and other tender vegetation which may be damaged.
U.S. Pat. No. 4,282,704 to Stevens discloses a filament mower in which the filament also continuously extends outwardly through the side walls of the housing, and in addition discloses a portion of the front wall which can be pivoted upwardly to expose the filament for trimming at the front of the mower. This mower possesses all the disadvantages of the previous idea, plus the considerable expense of the pivoting front wall, and the required mechanism to effect the pivoting of the front wall.
Patent application Ser. No. 121,819, assigned to The Toro Company, the assignee of the present invention, in one embodiment discloses a filament mower with cut off portions of the side walls which allows the filament to continuously extend beyond the side walls of the housing. A second embodiment discloses pivotable side walls which can be selectively lowered or raised for trimming. The first embodiment possesses the same disadvantages of a continually extended filament as disclosed in U.S. Pat. No. 4,232,505. The second embodiment possesses the same disadvantages as disclosed in U.S. Pat. No. 4,282,704, i.e., the considerable added expense of a specialized housing with pivoting side walls.
None of the three prior ideas are readily adaptable to use as a rigid blade mower, because of the obvious safety considerations caused by the cut out or pivotable portions of the housing, which expose the rigid blade outside the protection offered by the housing.
U.S. Pat. No. 4,201,034 to Frantello, discloses a mower wherein a bar or plate with a filament containing cylinder at each end replaces the blade. This device is adapted for cutting merely with the filament which extends from the cylinders, and the plate or bar carrying the cylinders is not designed for cutting, i.e., is not a blade. Similarly, U.S. Pat. No. 4,295,324, also to Frantello, discloses a head which replaces the conventional blade. This head carries filaments at its outer ends. However, these filaments are disposed in the plane of cut of the original blade. Since the plane of cut of the blade is contained within the housing for safety, this places the filaments of this invention also within the housing, thus precluding their being used to trim outside the housing.